Heat 3 tbsp. oil in a medium saucepan. Add onion and garlic and cook until soft. Stir in Arborio rice to coat, then add wine and cook until reduced, then add lobster pieces. Add stock, 2 cups at a time, for a total of 4 cups, and cook until rice is al dente and lobster is cooked through. If you run out of stock and need to add more liquid, use water. Add kosher salt and freshly ground black pepper, to taste.